According to the latex aggregation method, aggregation of latex is facilitated by an antigen, which is added as a sample and cross-links a plurality of latex-bound antibodies. This simple procedure allows for easy and rapid detection of an antigen. However, when the amount of the antigen is small, since it is difficult to generate cross-linking, a sufficient amount of latex cannot aggregate. Therefore, it has been difficult to detect a small amount of antigen. In addition, in manual measurement, there has been a problem in measured results which show large variations.
Thus, methods utilizing an enzyme-substrate reaction, such as ELISA and CLEIA, are widely adopted. In these methods, for example, a primary antibody that binds specifically to an antigen is bound to an antigen, and a secondary antibody having an enzyme is bound to this primary antibody. Then, an enzyme substrate is added and the reactivity of a reaction catalyzed by the enzyme is measured to detect or quantify an antigen.
According to these methods, by using a luminescent reagent as a substrate, for example, the high detectability of a luminous reaction after adding the substrate allows detection of a small amount of antigen.